/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.transforms.windowing;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.vendor.guava.com.google.common.base.Joiner;

import org.joda.time.Instant;



import java.util.Arrays;

import java.util.List;



import static com.bff.gaia.unified.vendor.guava.com.google.common.base.Preconditions.checkArgument;



/**

 * A composite {@link Trigger} that executes its sub-triggers in order. Only one sub-trigger is

 * executing at a time, and any time it fires the {@code AfterEach} fires. When the currently

 * executing sub-trigger finishes, the {@code AfterEach} starts executing the next sub-trigger.

 *

 * <p>{@code AfterEach.inOrder(t1, t2, ...)} finishes when all of the sub-triggers have finished.

 *

 * <p>The following properties hold:

 *

 * <ul>

 *   <li>{@code AfterEach.inOrder(AfterEach.inOrder(a, b), c)} behaves the same as {@code

 *       AfterEach.inOrder(a, b, c)} and {@code AfterEach.inOrder(a, AfterEach.inOrder(b, c)}.

 *   <li>{@code AfterEach.inOrder(Repeatedly.forever(a), b)} behaves the same as {@code

 *       Repeatedly.forever(a)}, since the repeated trigger never finishes.

 * </ul>

 */

@Experimental(Experimental.Kind.TRIGGER)

public class AfterEach extends Trigger {



  private AfterEach(List<Trigger> subTriggers) {

    super(subTriggers);

    checkArgument(subTriggers.size() > 1);

  }



  /** Returns an {@code AfterEach} {@code Trigger} with the given subtriggers. */

  @SafeVarargs

  public static AfterEach inOrder(Trigger... triggers) {

    return new AfterEach(Arrays.asList(triggers));

  }



  /** Returns an {@code AfterEach} {@code Trigger} with the given subtriggers. */

  public static AfterEach inOrder(List<Trigger> triggers) {

    return new AfterEach(triggers);

  }



  @Override

  public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {

    // This trigger will fire at least once when the first trigger in the sequence

    // fires at least once.

    return subTriggers.get(0).getWatermarkThatGuaranteesFiring(window);

  }



  @Override

  protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {

    return Repeatedly.forever(new AfterFirst(continuationTriggers));

  }



  @Override

  public String toString() {

    StringBuilder builder = new StringBuilder("AfterEach.inOrder(");

    Joiner.on(", ").appendTo(builder, subTriggers);

    builder.append(")");



    return builder.toString();

  }

}